This invention concerns quantum computers in which the qubits are closed systems, in that the particle or particles are confined within the structure. A “site” can be produced by any method of confining an electron or other quantum particle, such as a dopant atom, a quantum dot, a cooper pair box, or any combination of these. In particular the invention concerns a closed three-site quantum particle system. The state in the third site is weakly coupled by coherent tunneling to the first and second states, so that the third state is able to map out the populations of the first and second states as its energy is scanned with respect to the first and second states. In second and third aspects it concerns a readout method for a closed three-state quantum particle system.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A closed three-site quantum particle system, comprising: a first site in which energy is controllable; a second site in which energy is controllable; states in the first and second sites that are strongly coupled to each other by coherent tunnelling, and where a tunelling rate is controllable; and, a third site in which energy is controllable, the third site having a state that is weakly coupled by coherent tunnelling to the states in the first and second sites, so that the third state is able to map out populations of the first and second states as its energy is scanned with respect to the first and second states.
2. The closed three-site quantum particle system according to claim 1 , wherein the states in the first and second sites are a solid-state charge qubit with one particle shared between the first and second sites.
3. The closed three-site quantum particle system according to claim 2 , wherein the system is operated in the superposition basis with an integrated readout using the state of the third site as a probe state.
4. The closed three-site quantum particle system according to claim 3 , wherein Adiabatic Fast Passage (AFP) is employed as a readout mechanism, and during readout the AFP has trajectory.
5. The closed three-site quantum particle system according to claim 4 , wherein difference between the energy of the probe state and the energy of the qubit, and the tunnelling rate between the probe state and the qubit are modulated to effect AFP.
6. The closed three-site quantum particle system according to claim 4 , wherein the AFP trajectory is reversed to re-initialise the qubit into a known state.
7. The closed three-site quantum particle system according to claim 1 , wherein the energies and tunnelling rates are controlled using gate electrodes.
8. The closed three-site quantum particle system according to claim 7 , wherein voltages on the gate electrodes are controlled.
9. The closed three-site quantum particle system according to claim 7 , wherein a sensitive electrometer is used for reading out the population in the third state.
10. The closed three-site quantum particle system according to claim 9 , wherein the sensitive electrometer is realised by a single electron transistor (SET) which monitors charge in the third, weakly coupled, site.
11. The closed three-site quantum particle system according to claim 10 , wherein the sensitive electrometer is realised by a quantum point contact.
12. The closed three-site quantum particle system according to claim 1 , when used for readout from a quantum computer.
13. The closed three-site quantum particle system according to claim 1 , wherein alternatively, the first site involves a solid-state spin qubit, and the second site involves a reference spin and the state of the third site is used as a probe state.
14. The closed three-site quantum particle system according to claim 13 , wherein relative spins of the first and second sites are converted into charge distribution information.
15. The closed three-site quantum particle system according to claim 13 or 14 , wherein Adiabatic Fast Passage (AFP) is employed as a readout mechanisms, and during readout the AFP has trajectory.
16. The closed three-site quantum particle system according to claim 15 , wherein the difference between the energy of the probe state and the energy of the qubit, and the tunnelling rate between the probe state and the reference spin are modulated to effect AFP.
17. The closed three-site quantum particle system according to claim 16 , wherein the AFP trajectory is reversed to re-initialise the qubit into a known state.
18. The closed three-site quantum particle system according to claim 13 wherein the energies and tunnelling rates are controlled using gate electrodes.
19. The closed three-site quantum particle system according to claim 18 , wherein voltages on the gate electrodes are controlled.
20. The closed three-site quantum particle system according to claim 19 , wherein a sensitive electrometer is used for reading out the population in third state.
21. The closed three-site quantum particle system according to claim 20 , wherein the sensitive electrometer is realised by a single electron transistor (SET) which monitors charge in the third, weakly coupled, site.
22. The closed three-site quantum particle system according to claim 21 , wherein the sensitive electrometer is realised by a quantum point contact.
23. The closed three-site quantum particle system according to claim 13 , applied to readout from a quantum computer.
24. The closed three-site Quantum particle system according to claim 23 , wherein the quantum computer uses nuclear spin or electron spin qubits.
25. The closed three-site quantum particle system according to claim 1 , wherein the system is used with flux quanta or 2D electron gas, and a third state introduced for readout.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
August 10, 2004
January 20, 2009
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